H, Control Design for an Industrial Boiler

In the control of an industrial boiler system, multi-loop (decentralized) PI control is used because of its simplicity and the existence of simple on-line tuning rules. We show that such control schemes sacrifices robustness and performance of the overall system. In particular, under normal boiler operating conditions, we design a robust multivariable controller using the H, loop-shaping technique. For reason of implementation, we then reduce this controller to a multivariable PI structure. Both the H, controller and its PI approximation are tested extensively in the frequency domain as well as in the time domain, using a complex nonlinear simulation software; the results show that the designed controllers are superior in robustness and performance compared to the existing multi-loop controller. , '-.. characteristics, utility boilers are used to regulate the steam pressure, while CO boilers and OTSG boilers are used to track steam load and regulate the steam temperature, respectively. At present, utility boilers are controlled via a multiloop (decentralized) proportional plus integral (PI) type controller. This configuration, however, ignores the fact that there exist interactions among the variables to be regulated. The result is that under normal operation, the 90W header pressure exhibits oscillatory modes that the controller is unable to damped out as quickly as desired. This motivates the redesign of the utility boiler controllers to improve overall system performance.